To provide a treatment method and a treatment apparatus of organic wastes capable of stably and efficiently carrying out methane fermentation of organic solid wastes and solving instability at the time of high load.

After methane fermentation of organic solid wastes in a first methane fermentation tank 2, solid-liquid separation is carried out and the separated liquid is methane-fermented in a second methane fermentation tank 4. The separated sludge is turned back to the first methane fermentation tank 2.